1. Field of the Invention
This invention generally relates to methods and apparatus for spraying plural component materials without requiring the use of solvents to routinely flush or purge equipment or as part of the materials being dispensed.
2. Description of the Prior Art
Spray applied plural component thermoplastic and thermosetting materials have gained wide commercial acceptance as protective and decorative coatings. Similarly, spray applied foams are in widespread use throughout the world. Molded products produced from spray application equipment are also gaining greater acceptance and becoming popular in some industries. There is a large body of prior art with respect to these types of materials that usually come as two part formulations in which the respective parts chemically combine into finished form once dispensed from the spray application system. The cure rates and gel times vary widely for the various formulations from several hours to less than 10 seconds. In many formulations, the rates can be modified through the use of varying temperatures, types and amount of catalysts and other means.
Plural component formulations do occasionally come in 3, 4 or more parts but this is not the norm with the vast majority of plural component systems being two part systems. The respective components of a plural component system are often identified as a Part A and Part B respectively, with additional Part C, Part D, etc. in instances where there are more than the typical two fluid components involved. For purposes of this disclosure, the typical two part system and nomenclature will be used throughout although the applicants' intention is to not limit the scope of disclosure and claims to only two component systems by doing so. It is an accepted well known practice to introduce catalysts (accelerators), blowing agents, coloring agents, etc. as separate components in a plural component system rather than pre-blending such ingredients into one of the fluid components of a plural component system. However, describing these more complex systems can become cumbersome, particularly in the drawings, so the applicants respectfully ask readers to consider a plural component system as being defined herein as a formulation that comes in two or more parts.
Many formulations employ solvents in varying types and amounts either within the formulations themselves or to clean and purge some or all of the equipment components of the spraying systems known in the prior art. U.S. Pat. No. 4,695,618, issued to Norman R. Mowrer in 1987, discloses that a then “growing emphasis on compliance with government environmental and health regulations that limit both the type and amount of volatile organic compounds (VOC) has prompted coating manufacturers and end users to evaluate new coating technologies” (Col 1 Row 40-44). Since that time, manufacturers have produced an increasing number of formulations that are described in the art as being as much as 100% solids—a term used to describe the percentage of the ingredients that remain in the formulations after completion of the cure cycle. This confirms there has in fact been a long felt need to reduce or eliminate the use of said solvents and other volatile components from formulations and also from equipment purging and cleaning processes.
Manufacturers of formulations and equipment respectively are having difficulties developing new technologies that meet the tightening environmental and health requirements while meeting customer and end user demands for better solutions without increasing costs. In particular, eliminating the use of solvents has made it much more difficult to develop improved formulations that maintain 1:1 volumetric ratios with matched viscosities. The trend has been toward formulations that have widening ratios with 4:1 currently considered the maximum viable ratio. For the purposes of this disclosure, the standard ratios are: 1:1, 1.5:1, 2:1, 3:1 and 4:1 with ratios wider than that considered non-standard. Many practitioners consider ratios beyond 2:1 to be non-standard while recognizing that more formulations with wider ratios are coming into use.
It is desired to have spraying systems that go beyond this to accommodate in excess of 10:1 for some formulations. Generally, the widely held perception is that the further a ratio moves from 1:1, the more difficult it becomes to successfully mix and dispense the material. Viscosities are similarly becoming more divergent, generally increasing, with formulations known in the art that have viscosities increasing to as much as 1,000,000 cP (centipoise). In comparison, other materials have much lower viscosities, as little as 50 cP. It has therefore become a common practice to include elaborate heating systems to decrease the viscosity of thick materials such that they can be successfully pumped, mixed and dispensed using spraying technology. As a point of clarification, the term “spraying” is being used for expediency, while other applying or dispensing techniques are also envisioned.
U.S. Pat. No. 5,344,490, issued to Peter Paul Roosen et al. in 1994, discloses a plasticised gypsum composition that includes plural component formulations that have volumetric ratios ranging between 4:1 to 9:1 and large differences in viscosity between the respective Part A and Part B components. Roosen is one of the applicants herein and the disclosure of the '490 patent is incorporated herein by reference. Roosen '490 formulation Example 1 is for a plural component gypsum composition that contains 41% PBW (parts by weight) gypsum in total and is typically prepared in two parts with Part A being the gypsum and various other ingredients totaling 83% PBW and Part B being the balance 17% isocyanate. This 5:1 PBW ratio translates to a volumetric ratio of approximately 4.5:1 which is not a standard industry ratio and has therefore been difficult to dispense by means of a solvent-free spray application using conventional off the shelf equipment. Roosen and others were forced to use non-spraying means to dispense the formulations due to numerous failed attempts to disperse the material by means of a suitable spraying system.
The Roosen '490 patent also discloses a formulation in which the gypsum composition contains 75% PBW gypsum and a much smaller percentage of isocyanate (less than 7% PBW) that is produced into various finished products including products similar to those prepared using the above Example 1 formulation. This Example 2 formulation is quite similar to the Example 1 formulation with the increased amount of gypsum being the primary difference. It has always been one of Roosen's objectives to find a suitable means to spray apply the Example 1 formulation that contains 41% PBW gypsum and, if possible, to use spraying systems to apply formulations that have higher percentages of gypsum, approaching the 75% PBW gypsum level of the Example 2 formulation. Those efforts of almost 20 years have consistently failed. This failure is partly due to his lack of willingness to incorporate petrochemical solvents into the formulation or as part of a purging or routine flushing system for a spraying system.
The above Roosen formulations and products derived from them have been recognized in Canada and other countries as excellent examples of “green” and sustainable technologies that have minimal adverse impact on the environment. There have been further developments to replace the petrochemical derived isocyanate component with other materials to further enhance the green aspects. In fact, in 2010, Roosen was awarded a $100,000 cash prize for having won Canada's national “Greenvention” competition in front of millions of television viewers and he has been named the country's top “Eco-preneur”. He has steadfastly refused to accept any proposed method to dispense formulations using spraying equipment that uses petrochemical solvents as either ingredients or part of a routine purging system, both of which are among common and widespread current industry practices.
As an interesting contrast, to the Roosen '490 formulations, Mowrer '618 reveals a series of two-component, solvent-free polyurethane compositions which may be combined at substantially 1:1 ratio by volume, and applied with commercially available, plural component, airless spraying equipment at ambient temperatures. He goes to some length in describing his formulations and reasons for conforming to various perceived technical limitations. His formulations appear to be composed of well marketed standard petrochemical ingredients produced by a relatively small number of well established chemical manufacturers. We believe that approach of conforming to a narrow band of technical constraints has the disadvantage of limiting the ability of practitioners to invent new and useful products of potentially greater value to customers and end users.
Furthermore, it makes it much more difficult to develop sustainable and environmentally sound solutions. Mowrer's approach, however, has been and continues to be preferred by equipment manufacturers.
Another important variable is pressure. Modern plural component spraying equipment has been engineered to operate at increasing pressures, currently in excess of 7,000 psi (50,000 kPa) for some systems. This is largely due to the need to successfully proportion, mix, and disperse solvent-free formulations with high viscosity components. The ability to operate at lower pressures is preferred to increase equipment life and operator safety while reducing operating and maintenance costs. Mowrer and others suggest system pressure and viscosity limits of 3,000 psi (21,000 kPa) and 1,000 cP (centipoises) respectively. Graco Minnesota Inc. is a well established Minneapolis based manufacturer of plural component spray equipment. In a 2011 Graco technical manual for the company's Fusion™ Solvent Purge Plural-Component Gun, there is an explicit instruction to balance the gauges at the required pressure. This Graco gun is a relatively heavy apparatus that is awkward and difficult to use due to its excessive weight and bulky size and it therefore has limited utility. In U.S. Pat. No. 7,744,019 issued to Matthew Merchant, there is an explicit expressed requirement to introduce the two respective components of a two part system into the mixing tube at the same pressures, which in this case is approximately 3,000 psi (21,000 kPa).
There is a strong tendency toward keeping viscosities, ratios and pressures matched that is well established in the prior art.
Although there has been a trend toward reducing the amount of solvent that is used within the formulations, the opposite has been the case for cleaning and purging plural component spray system equipment. There is a tremendous amount of prior art pointing toward likely millions of gallons (liters) a year of solvents used to clean and purge said equipment. For instance, it is common knowledge that for many epoxy coating systems of the 100% solids type, it typically takes approximately 5 gallons (20 liters) of solvent to purge and clean the equipment after each use. For a typical use of 50 gallons (200 liters) of said epoxy coating, that amount of solvent would be equivalent to having the formulation containing 10% solvent within it. It would appear that much of the benefit of reducing the solvent within the formulations is lost when taking account of the purging and cleaning requirements.
U.S. Pat. Nos. 7,918,369 5,678,764 6,544,204 5,178,326 4,760,956 4,695,618 4,967,956 6,811,096 and 6,824,071 are among the many examples of prior art explicitly applying solvent purging and cleaning systems. Graco appears to have substantial interest in many of these above patents and in publications such as WO 2009/036129 directed toward solvent injection systems. The company's current Fusion™ Solvent Purge Plural-Component Gun for which it claims patent pending status appears to represent the state of the art.
The solvent purge or flush spraying systems currently in widespread use typically employ a set of ratio proportioning pumps that deliver two or more respective components of a plural component fluid formulation under pressure to a manifold where the two streams are combined after which the combined fluids are forced through one or more static mixing elements located in the fluid path, through a single hose or tube often called a whip then through a spray gun which dispenses the mixed material. Static mixers can also be located further downstream and are sometimes found in the gun itself or at more than one location in the mixed fluid pathway. A separate solvent pump delivers a stream of solvent which is pumped through the manifold, static mixing elements, whip and gun at the end of each operating cycle to purge any mixed material from the system before such mixed material cures and clogs one or more parts of the system. U.S. Pat. No. 5,178,326, issued to Timothy S. Kukesh et al., is directed to such a system with the inclusion of additional compressed air impingement acting on the mixed material after exiting the spraying orifice of the spray gun. Kukesh '326 illustrates this conventional solvent purge approach quite well.
There is also prior art describing spraying equipment that has been designed for mixing in the gun very close to the spraying orifice. The mixing of the plural component formulations occurs in a small mixing chamber through the impingement mixing of plural fluid streams that exit the spraying orifice, sometimes referred to as a spray tip, very near the location of the impingement mixing. For clarification, the plural components are brought into the gun separately and mixed very close to the spray tip. U.S. Pat. No. 7,527,172, issued to Jonathan R. McMichael, is directed toward improvements in such a plural component (two components) mixing and dispensing apparatus. The McMichaels '172 apparatus requires the volumetric proportioning ratio to be near or at 1:1, the fluid viscosities of the respective two fluids to be relatively low and closely matched and the pressures to be relatively closely matched because it relies on impingement mixing to mix the two fluid components. These types of spray guns are primarily used for fast set urethane foams that normally cure in a matter of seconds. Many of the impingement mixing type guns that are typically used for fast setting urethane foams and ureas also employ solvent purging although it is not as necessary as for the more common non-impingement mixing type of gun where solvent usage is widespread. Some of the impingement mixing type guns including the one disclosed in McMichaels '172 use air to purge the relatively small amount of mixed material that needs to be quickly purged at the end of each use of the gun. Guns of this type are not effectively being used for non-standard ratio formulations, particularly where there are high viscosity fluids involved. Attempts to use impingement mixing guns for such materials generally produce inadequate results due to insufficient mixing, poor spray pattern, clogging or a combination of these.
U.S. Pat. No. 3,799,403, issued to Richard O. Probst et al., the disclosure of which is incorporated herein by reference, discloses a spray gun in which the mixing chamber is movable with respect to the housing as a practical and simple means of stopping and starting the flow of plural fluid components and also so that a gas such as compressed air can be used to purge the mixing chamber of the mixed residue of plural component material upon termination of the dispensing operation. Although such guns have been in use for many years, it is difficult to obtain consistent, high quality mixing of the fluid components, especially when the ratios, viscosities and/or pressures are uneven.
Another strategy for purging plural component system is to shut off one of the fluid components and let another fluid component continue to flow to purge mixed material from the system. This is often ineffective due to what is sometimes referred to as a crossover effect, whereby the purge fluid flows in a reverse direction toward where the fluid component that has been shut off normally enters the mix chamber. This is where mixed material builds up and eventually clogs or impedes flow.